The invention relates to an energy delivery system for performing myocardial revascularization on a beating heart of a patient.
Transmyocardial revascularization (TMR) is a surgical treatment for cardiovascular disease. Present TMR procedure is an open chest technique (thoracotomy) that uses a laser beam to drill holes through the myocardium, typically into the left ventricle. These holes or channels extend through the entire heart wall thickness from the outside through to the ventricle. The openings of the channels on the outside surface of the heart heal due to external pressure from the surgeon, but the channels are believed to remain open on the inside, allowing blood to enter the heart wall tissue from the ventricle.
In another approach myocardial revascularization can be performed using a catheter introduced percutaneously so that the tip of the catheter is inside a chamber of the heart, typically the left ventricle, where the holes or channels can be created from the inside toward but not through the outside of the heart. This approach is also known as endocardial laser revascularization (ELR), percutaneous myocardial revascularization (PMR), and direct myocardial revascularization (DMR). The channels are drilled with a laser beam introduced through the catheter.
Certain problems are presented when laser revascularization is done on a beating heart. A beating heart presents a moving target, which can make it difficult to accurately and consistently form channels of a desired depth and size. The heart also is extremely sensitive to a laser pulse at certain times during its cycle. A laser pulse striking the heart at the T time of an electrocardiogram (ECG) signal could cause the heart to fibrillate and result in heart failure. While one could stop the heart during the process of TMR, this poses other risks to the patient and complicates the operating procedure. The heart must be cooled and the patient connected to a heart-lung machine.
However, the risk of inducing a beating heart to fibrillate is greatly reduced when the laser is fired only during the refractory period of the heart cycle between the R and T waves of the ECG signal. An additional benefit of firing the laser only between the R and T waves is that this is the period of the heartbeat cycle during which the heart is most still and channels can be formed most accurately. Rudko U.S. Pat. No. 5,125,926 describes a heart-synchronized pulsed laser system that fires a laser only during the refractory period of the heartbeat cycle. The patent describes an open chest procedure using an articulated optical arm or a fiber optic element to deliver the laser beam to a surface of the heart.
Aita U.S. Pat. No. 5,389,096 discloses a percutaneous TMR procedure in which a steerable heart catheter is guided from the femoral artery via the abdominal artery into the left ventricle. The laser energy is delivered through the working channel of the catheter by a fiber optic delivery system.
WO 98/27877 and Eggers U.S. Pat. No. 5,860,951 describe using electrical current pulses delivered from electrodes on a catheter (for percutaneous access) or handpiece (for external access) to create channels in a TMR procedure.
The above-referenced patents and PCT publication are hereby incorporated by reference in their entireties.
In one aspect, the invention features, in general, a heart-synchronized energy delivery system for performing myocardial revascularization on a beating heart of a patient. The system includes an energy pulse source that produces electrical pulses sufficient to create channels in a wall of the heart, an energy pulse source delivery system (e.g., a handpiece or catheter with an electrode for delivering the pulses to a heart wall surface), a heart cycle sensor, and a controller that is responsive to the heart cycle sensor for firing the energy pulse system to provide energy to strike the beating heart only within a safe time period during a heart beat cycle. The safe time period is automatically determined by the controller with respect to the cyclical event.
In another aspect, the invention features, in general, an energy delivery system for performing myocardial revascularization on a heart of a patient. The system includes an energy pulse source that produces electrical pulses and an energy pulse delivery system that includes a support structure that is expandable from a retracted position in a catheter to an expanded position in which the structure has portions adjacent to a plurality of locations on an interior surface of a wall of a chamber of the heart. The support structure carries a plurality of electrodes that deliver electrical pulses to respective locations on the wall of the heart to form respective channels in the wall of the heart.
In another aspect, the invention features, in general, an energy delivery system for performing myocardial revascularization. The system includes an energy pulse source that produces electrical pulses, and an energy pulse delivery system that has an electrode for delivering the electrical pulses to a desired location for a channel in the wall of the heart of a patient. The system also includes an electromotion mechanism for advancing the electrode into the channel as, or shortly after but not before, the channel regions are formed. The mechanism also retracts the electrode from the channel that has been formed.
In another aspect, the invention features, in general, an energy delivery system for performing myocardial revascularization. The system includes an energy pulse source and an energy pulse delivery system with a delivering end for delivering the energy pulses to desired locations for channels in the wall of a heart of a patient. The system may also include a temperature sensor sensing temperature of the delivery end or of the heart wall during creation of a channel, and the energy pulse source is responsive to the temperature in controlling the production of energy pulses.
In another aspect, the invention features, in general, an energy delivery system for performing myocardial revascularization on a heart of a patient. The system includes an energy pulse source and an energy pulse delivery system for delivering energy pulses to create channels in a wall of a heart of a patient. The system also includes a cooling system that via thermal conductivity removes heat generated during creation of channels in the heart of a patient.
In another aspect, the invention features, in general, an energy delivery system for performing myocardial revascularization including an energy pulse source that produces energy pulses sufficient to create channels in a wall of the heart, and an energy pulse delivery system for delivering the energy pulses to desired locations for channels in a wall of a heart. The energy pulse source programmably varies duty cycle, amplitude, and duration of the energy pulses. The flow rate of a cooling system or temperature of a cooling substance could also be adjusted.
In another aspect, the invention features, in general, an energy delivery system for performing myocardial revascularization on a heart of a patient. The system includes an energy pulse source and an energy pulse delivery system for delivering energy pulses to create channels in a wall of a heart of a patient. The system also includes a sensor (e.g., an ultrasound sensor) that senses a dimension of the myocardium of the heart (e.g., its thickness or the depth of a channel being formed), and the energy pulse source and the energy pulse delivery system are responsive to the sensor to control the formation (e.g., the depth) of the channel.
In other aspects of the invention, the invention features, in general, a heart-synchronized energy delivery system for performing myocardial revascularization on a beating heart of a patient the includes a heart cycle sensor that senses blood pressure, ventricular contraction, or acoustics related to ventricular contraction. Blood pressure measurements include ventricular, atrial, aortic, and pulminary artery/pulminary capillary wedge pressures.
Particular embodiments of the invention may include one or more of the following features. The electrical pulses are pulses of alternating current, preferably radio frequency or microwave. The support structure for multiple electrodes is a spiral or is basket shaped. A single pulse or a plurality of pulses are used to create each channel, and the electromotion mechanism advances each electrode between or within the pulses. The heart cycle sensor senses an electrical signal (e.g., a standard or local ECG signal or a pacemaker signal) that causes the heart to beat. The safe time period is a period in which firing of the energy pulse system will not cause fibrillation of the heart. The safe time period is a period during which the heart is less sensitive electrically. The energy pulse system controller includes an operator input device (e.g., a foot actuated switch) that provides an activation signal to activate firing of the energy pulse system, and the energy pulse system controller fires the energy pulse system during the safe time period subsequent to receiving the activation signal. The energy pulse delivery system includes a handpiece having an end adapted to contact the outside surface of a wall of the heart. Alternatively the energy pulse delivery system delivers the energy pulses to an inside surface of a wall of the heart, via an energy conduit. The energy conduit may consist of an electrically conductive probe and wire connected to the probe. The probe may be made of beryllium copper or another conductive material. The wire may be constructed of kink resistant material such as a superelastic alloy, for example, Nitinol.
The invention also includes methods of performing myocardial revascularization relating to the aspects and features of the invention described above.
Embodiments of the invention may include one or more of the following advantages. Fibrillation is avoided by operating only within a safe time period. In addition, the energy pulses can be desirably applied to the heart when it is relatively immobile to promote accuracy. The heart cycle can desirably be determined by monitoring one of a variety of different parameters. A plurality of channels can be provided at one time, reducing the time of the procedure and stress on the patient. The delivery of energy pulses and the rate of advancement can or may be programmably controlled to provide optimal conditions and avoid thermal and/or mechanical damage to the heart tissue. A temperature sensor can sense either the temperature of a probe or the temperature of tissue surrounding the channel being formed and the procedure can be controlled to avoid heat caused tissue damage. The temperature of the probe can be lowered and maintained using an integral cooling system and adjustment of energy parameters that may include amplitude, duration, and duty cycle.
Other advantages and features of the invention will be apparent from the following description of particular embodiments of the invention and from the claims.